1. Field of the Invention
The present invention relates to an apparatus for molding products. More particularly, the present invention relates to a formwork, a means for clamping the formwork and a means for actuating the clamping of the formwork.
2. Description of the Prior Art
Techniques for clamping a formwork are described in Japanese Patent Publication Nos. 57-44447, 57-45645 and 58-49372. In these techniques, angle members are secured to joining portions of a pair of two molds, constituting a formwork, thereby to form protruding pieces. The pair of protruding pieces are clamped to each other by a number of wedges disposed along a longitudinal direction of the formwork. The number of wedges are connected in series. By pulling one end of the series of wedges in the longitudinal direction of the formwork, the wedges are moved as a unit so that the protruding pieces are clamped at each wedge portion along the longitudinal direction of the formwork.
However, in these techniques, both the action of clamping the formwork and the action of maintaining the clamped condition are performed by the wedges. As a result, the force exerted by the wedges on both the protruding pieces, to bring the protruding pieces into engagement, becomes necessarily large. Therefore, a large force is required to pull the wedges, since the frictional force at the wedge surfaces is high. Accordingly, since an expansion is caused in the member connecting the wedges, the intervals of the wedges and the intervals of positions at which the wedges impart the forces are deviated and not coincident with each other. Thus, drawbacks have been encountered in which it becomes impossible to clamp uniformly along the longitudinal direction. At the same time, the correction of the wedge intervals must be made while correcting relative positions with respect to other wedges, which requires many man-hours.
Furthermore, the direction of the pulling of the wedges and the direction of force exerted to bring the pair of protruding pieces into engagement are different from each other by 90 degrees. As a result, since the turn of the direction of the force is effected on the surfaces of the wedges, the pulling force of the wedges is greatly reduced.
Moreover, in order to transmit the pulling force across the series of the wedges, it is necessary to connect the wedges throughout the formwork continuosly in the longitudinal direction by a member. Therefore, it is necessary to form a hole in a circular ring (a so-called "tire") for rotating the formwork, or in a protruding portion of a reinforcing rib or the like. Thus, the drawbacks are the inefficiency in wasted man-hours and the degraded strength of the ring or rib.